Heterocycle catalyzed electrochemical process

ABSTRACT

A method for heterocycle catalyzed electrochemical reduction of a carbonyl compound is disclosed. The method generally includes steps (A) to (C). Step (A) may introduce the carbonyl compound into a solution of an electrolyte and a heterocycle catalyst in a divided electrochemical cell. The divided electrochemical cell may include an anode in a first cell compartment and a cathode in a second cell compartment. The cathode generally reduces the carbonyl compound to at least one aldehyde compound. Step (B) may vary which of the aldehyde compounds is produced by adjusting one or more of (i) a cathode material, (ii) the electrolyte, (iii) the heterocycle catalyst, (iv) a pH level and (v) an electrical potential. Step (C) may separate the aldehyde compounds from the solution.

This invention was made with government support under Grant No.CHE-0911114 awarded by the National Science Foundation. The governmenthas certain rights in this invention.

FIELD OF THE INVENTION

The present invention relates to electrochemical processing generallyand, more particularly, to a method and/or apparatus for implementing aheterocycle catalyzed electrochemical process.

BACKGROUND OF THE INVENTION

Alcohols and organic chemicals with hydroxyl and carbonyl functionalgroups are important to industrial processes and the production of lightalcohol fuels. At present, several different processes are used forproduction of alcohols. Most alcohols are produced from oil or naturalgas, while some including ethanol and pentanol are producedbiologically. Hydroxyl groups are often introduced to organic moleculesvia catalytic hydrogenation of aldehydes or acid catalyzed hydration ofalkenes. Some specific examples include methanol, which is produced bycatalytic conversion of synthesis gas at high temperature and pressure.Ethanol is produced by acid catalyzed hydration of ethylene or byvarious microorganisms via fermentation of sugars.

Two major processes exist for propanol production. Acid catalyzedhydration of propylene is performed, resulting in a mixture of bothisopropanol and n-propanol. Another process to make n-propanol ishydroformylation of ethylene to propionaldehyde followed by catalytichydrogenation of propionaldehyde to n-propanol. N-butanol is produced ina manner similar to that of n-propanol. Propylene is converted tobutyraldehyde via hydroformylation. The butyraldehyde is thencatalytically hydrogenated to n-butanol. Sec-butanol is produced in amanner similar to ethanol, by the acid catalyzed hydration of 1-buteneor 2-butene. Isomers of pentanol are primarily produced by thedistillation of fusel oil. Fusel oil is a product of some biologicalfermentation processes. Hexanol and higher order alcohols are commonlyproduced by oligomerization of ethylene, which results in a mix ofdifferent products separated via distillation.

At present, many different techniques are currently used to create otherorganic products. Biological processes, such as fermentation of sugars,produce ethanol or fusel oil. The Fischer-Tropsch process is used forconversion of synthesis gases to organic molecules. Hydroformylation ofalkenes is followed by catalytic hydrogenation to alcohols or alkanes.Polymerization of alkenes results in organic products. Electrochemicalhydrodimerization of alkenes, notably the Monsanto process, producesadiponitrile.

Existing electrochemical and photochemical processes/systems have one ormore of the following problems that prevent commercialization on a largescale. Selectively producing some alcohols, notably isopropanol,butanol, pentanol, and higher order alcohols is difficult. Selectivelyreducing carboxyl or carbonyl groups is also difficult withoutundesirable side reactions such as hydrogenation of aromatic moleculesor heterocycles. Many existing processes, notably the Fischer-Tropschprocess, make multiple products that are subsequently separated.Production of some aldehydes and alcohols use multi-step reactions thatcollectively have low energy efficiency. Likewise, hydrodimerizationwithout a catalyst can be very inefficient. Existing reaction pathwaysuse high heat, high temperature and/or highly acid environments. Theheat conditions result in the use of expensive materials for thereactors. Many existing processes, both thermally and electrochemicallydriven, also use alkenes as a starting material.

SUMMARY OF THE INVENTION

The present invention concerns a method for heterocycle catalyzedelectrochemical reduction of a carbonyl compound. The method generallyincludes steps (A) to (C). Step (A) may introduce the carbonyl compoundinto a solution of an electrolyte and a heterocycle catalyst in adivided electrochemical cell. The divided electrochemical cell mayinclude an anode in a first cell compartment and a cathode in a secondcell compartment. The cathode generally reduces the carbonyl compound toat least one aldehyde compound. Step (B) may vary which of the aldehydecompounds is produced by adjusting one or more of (i) a cathodematerial, (ii) the electrolyte, (iii) the heterocycle catalyst, (iv) apH level and (v) an electrical potential. Step (C) may separate thealdehyde compounds from the solution.

The objects, features and advantages of the present invention includeproviding a method and/or apparatus for implementing a heterocyclecatalyzed electrochemical process that may (i) reduce carbonyl groups toaldehydes, (ii) reduce aldehydes to alcohols, (iii) reduce keto groupsto hydroxyl groups, (iv) support heterocycle catalyzed electrochemicalprocessing at a commercial level, (v) operate at atmospheric pressure,(vi) operate at ambient temperature, (vii) use water as a solvent,(viii) process at a mild pH, (ix) selectively electrohydrodimerizecarbonyl-containing compounds to a variety of organic chemicals and/or(x) provide stable processing over time.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the presentinvention will be apparent from the following detailed description andthe appended claims and drawings in which:

FIG. 1 is a block diagram of a system in accordance with a preferredembodiment of the present invention;

FIG. 2 is a diagram illustrating reductions of two-carbon and higherstarting materials;

FIG. 3 are formulae of example hydrodimerization reactions;

FIG. 4 is a table illustrating relative product yields for differentcathode material, catalyst and cathode potential combinations;

FIG. 5 is a formula of an aromatic heterocyclic amine catalyst;

FIGS. 6-8 are formulae of substituted or unsubstituted aromatic 5-memberheterocyclic amines or 6-member heterocyclic amines;

FIG. 9 is a flow diagram of an example method used in electrochemicalexamples; and

FIG. 10 is a flow diagram of an example method used in photochemicalexamples.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Some embodiments of the present invention relate to heterocyclecatalyzed reduction of keto groups to hydroxyl groups, carboxylic acidsto more reduced carboxylic acids, carboxylic acids to aldehydes and/oraldehydes to alcohols. Some embodiments generally relate tohydrodimerize of carbonyl compounds. The methods generally includeelectrochemically and/or photoelectrochemically reducing in an aqueous,electrolyte-supported divided electrochemical cell that includes ananode (e.g., an inert conductive counter electrode) in a cellcompartment and a conductive or p-type semiconductor working cathodeelectrode in another cell compartment. A catalyst may be included tohelp produce a reduced product. The reactants may be continuouslyintroduced into the cathode electrolyte solution to saturate thesolution.

For electrochemical reductions, the electrode may be a suitableconductive electrode, such as Al, Au, Ag, C, Cd, Co, Cr, Cu, Cu alloys(e.g., brass and bronze), Ga, Hg, In, Mo, Nb, Ni, Ni alloys, Ni—Fealloys, Sn, Sn alloys, Ti, V, N, Zn, stainless steel (SS), austeniticsteel, ferritic steel, duplex steel martensitic steel, Nichrome, elgiloy(e.g., Co—Ni—Cr), degenerately doped p-Si, degenerately doped p-Si:Asand degenerately doped p-Si:B. Other conductive electrodes may beimplemented to meet the criteria of a particular application. Forphotoelectrochemical reductions, the electrode may be a p-typesemiconductor, such as p-GaAs, p-GaP, p-InN, p-InP, p-CdTe, p-GaInP₂ andp-Si. Other semiconductor electrodes may be implemented to meet thecriteria of a particular application.

Before any embodiments of the invention are explained in detail, it isto be understood that the embodiments may not be limited in applicationper the details of the structure or the function as set forth in thefollowing descriptions or illustrated in the figures of the drawing.Different embodiments may be capable of being practiced or carried outin various ways. Also, it is to be understood that the phraseology andterminology used herein is for the purpose of description and should notbe regarded as limiting. The use of terms such as “including,”“comprising,” or “having” and variations thereof herein are generallymeant to encompass the item listed thereafter and equivalents thereof aswell as additional items. Further, unless otherwise noted, technicalterms may be used according to conventional usage.

In the following description of methods, process steps may be carriedout over a range of temperatures (e.g., approximately 10° C. (Celsius)to 50° C.) and a range of pressures (e.g., approximately 1 to 10atmospheres) unless otherwise specified. Numerical ranges recited hereingenerally include all values from the lower value to the upper value(e.g., all possible combinations of numerical values between the lowestvalue and the highest value enumerated are considered expressly stated).For example, if a concentration range or beneficial effect range isstated as 1% to 50%, it is intended that values such as 2% to 40%, 10%to 30%, or 1% to 3%, etc., are expressly enumerated. The above may besimple examples of what is specifically intended.

Referring to FIG. 1, a block diagram of a system 100 is shown inaccordance with a preferred embodiment of the present invention. Thesystem (or apparatus) 100 generally comprises a cell (or container) 102,a liquid source 104, a power source 106, a reactant source 108, anextractor 110 and an extractor 112. A product may be presented from theextractor 110. An output gas may be presented from the extractor 112.Another output gas may be presented from the cell 102.

The cell 102 may be implemented as a divided cell. The divided cell maybe a divided electrochemical cell and/or a divided photochemical cell.The cell, 102 is generally operational to reduce carbonyl compoundsand/or carboxyl group compounds (e.g., reactants) to aldehyde, alcohols,hydroxyl groups and/or organic products containing keto groups. Thereactants may also be reduced to methanol, ethanol, propanol, pentanol,hexanol and septanol. The cell 102 may also be operational tohydrodimerize carbonyl compounds to butanone (methyl ethyl ketone),butanol, octanone and/or octanol. The carbonyl compounds may include,but are not limited to, aldehydes and carboxylic acids. The reactionsgenerally takes place by introducing the reactants into an aqueoussolution of an electrolyte in the cell 102. A cathode in the cell 102may hydrodimerize and/or reduce the reactants into one or more organiccompounds.

The cell 102 generally comprises two or more compartments (or chambers)114 a-114 b, a separator (or membrane) 116, an anode 118 and a cathode120. The anode 118 may be disposed in a given compartment (e.g., 114 a).The cathode 120 may be disposed in another compartment (e.g., 114 b) onan opposite side of the separator 116 as the anode 118. An aqueoussolution 122 may fill both compartments 114 a-114 b. A catalyst 124 maybe added to the compartment 114 b containing the cathode 120.

The liquid source 104 may implement a water source. The liquid source104 may be operational to provide pure water to the cell 102.

The power source 106 may implement a variable voltage source. The source106 may be operational to generate an electrical potential between theanode 118 and the cathode 120. The electrical potential may be a DCvoltage.

The reactant source 108 may implement a keto group, carbonyl compound,carboxyl group compound and/or aldehyde source. The source 108 isgenerally operational to provide the reactants to the cell 102. In someembodiments, the reactants are introduced directly into the compartment114 b containing the cathode 120.

The extractor 110 may implement an organic product extractor. Theextractor 110 is generally operational to extract (separate) organicproducts (e.g., acetaldehyde, acetone, butanone, 2-butanol, n-butanol,ethanol, glyoxal, glyoxylic acid, methanol, octanone, octanol, oxalicacid, propanol, propioin and the like) from the electrolyte 122. Theextracted organic products may be presented through a port 126 of thesystem 100 for subsequent storage and/or consumption by other devicesand/or processes.

The extractor 112 may implement an oxygen extractor. The extractor 112is generally operational to extract oxygen (e.g., O₂) byproducts createdby the reactions. The extracted oxygen may be presented through a port128 of the system 100 for subsequent storage and/or consumption by otherdevices and/or processes. Any other excess gases (e.g., hydrogen)created by the reactions may be vented from the cell 102 via a port 130.

In the process described, water may be oxidized (or split) to protonsand oxygen at the anode 118 while organic molecules containing acarbonyl or carboxyl group are hydrodimerized and sometimes reduced atthe cathode 120. The electrolyte 122 in the cell 102 may use water as asolvent with any salts that are water soluble and with a heterocyclecatalyst 124. The catalysts 124 may include, but are not limited to,azoles, imidazoles, indoles, pyridine, pyrrole, thiazole and furan.Examples of the heterocyclic compounds catalysts 124 may be pyridine,imidazole, pyrrole, thiazole, furan, thiophene and the substitutedheterocycles such as amino-thiazole and benzimidazole. Cathode materialsgenerally include any conductor. Any anode material may be used. Theoverall process is generally driven by the power source 106.Combinations of cathodes 120, electrolytes 122, introduction of thecarbonyl or carboxyl group to the cell 102, pH levels and electricpotential from the power source 106 may be used to control the reactionproducts of the cell 102. Organic products resulting from the reactionsmay include, but are not limited to, alcohols, aldehydes, organicmolecules containing hydroxyl groups and/or organic products containingketo groups.

In some nonaqueous embodiments, the solvent may include methanol,acetonitrile, and/or other nonaqueous solvents. The electrolytesgenerally include tetraalkyl ammonium salts and a heterocyclic catalyst.In a system containing nonaqueous catholyte and aqueous anolyte, theproducts generally include all of the products seen in aqueous systemswith higher yields.

Experiments were conducted in one, two and three-compartmentelectrochemical cells 102 with a platinum anode 118 and SaturatedCalomel Electrode (SCE) as the reference electrode. The experiments weregenerally conducted at ambient temperature and pressure. Reactants wereintroduced into the cells during the experiments. A potentiostat or DCpower supply 106 provides the electrical energy to drive the process.Cell potentials ranged from 1.5 volts to 4 volts, depending on thecathode material. Half cell potentials at the cathode ranged from −1volt to −2 volts relative to the SCE, depending on the cathode materialused. Products from the experiments were analyzed using gaschromatography and a spectrometer.

Referring to FIG. 2, a diagram illustrating reductions of two-carbon andhigher starting materials is shown. Complex molecules, such as oxalicacid (a carboxylic acid) may be reduced to a simpler glyoxylic acid (aC2 carboxylic acid). The glyoxylic acid may be further reduced toglyoxal (a dialdehyde). Furthermore, the glyoxal may be reduced toacetaldehyde (an aldehyde). The acetaldehyde is generally reducible toethanol (a primary alcohol). Other aldehydes may include, but are notlimited to, formaldehyde, butanal and benzaldehyde. Other alcohols mayinclude, but are not limited to, methanol, 2-butanol, n-butanol,propanol, and propioin. The process is controlled to get a desiredproduct by using combinations of specific conductive cathodes,catalysts, electrolytes, surface morphology of the electrodes, pH levelsand/or introduction of reactants relative to the cathode. Faradaicyields for the products generally range from less than 1% to more than90% with the remainder generally being hydrogen.

Referring to FIG. 3, formulae of example hydrodimerization reactions areshown. Formula (1) generally illustrates a hydrodimerization of twoacetaldehyde molecules (e.g., C₂H₄O) into a butanone molecule (e.g.,C₄H₈O) and half of an oxygen (e.g., O₂) molecule. Formula (2) mayillustrate a hydrodimerization of two acetaldehyde molecules and twohydrogen ions (e.g., H⁺) into a butanol molecule (e.g., C₄H₉OH) and halfof an oxygen molecule. Formula (3) may show a hydrodimerization of twobutyric acid molecules (e.g., C₄H₈O₂) and two hydrogen ions into anoctanol molecule (e.g., C₈H₁₈O) and one and a half oxygen molecules.Formula (4) generally illustrates a hydrodimerization of two butyricacid molecules into a 2-octanone molecule (e.g., C₈H₁₆O) and one and ahalf oxygen molecules.

Referring to FIG. 4, a table illustrating relative product yields fordifferent cathode material, catalyst and cathode potential combinationsare shown. Lower pH generally favors reduction of a carbonyl groupwithout dimerization, for instance, the reduction of formic acid tomethanol. Aldehydes may be more likely to reduce to alcohols withoutdimerization. Carboxylic acids and dialdehydes may be more likely todimerize, with the exception of formic acid. Faradaic yields generallyimprove with more negative cathodic potential, particularly fordimerization. Any N-containing heterocycle may be used as a catalyst.4,4′ bipyridine was generally found to be an effective catalyst.Conversion rates generally improve with catalyst concentrations inexcess of 50 millimolar (mM).

Referring to FIG. 5, a formula of an aromatic heterocyclic aminecatalyst is shown. The ring structure may be an aromatic 5-memberheterocyclic ring or 6-member heterocyclic ring with at least one ringnitrogen and is optionally substituted at one or more ring positionsother than nitrogen with R. L may be C or N. R1 may be H. R2 may be H ifL is N or R2 is R if L is C. R is an optional substitutent on any ringcarbon and may be independently selected from H, a straight chain orbranched chain lower alkyl, hydroxyl, amino, pyridyl, or two R's takentogether with the ring carbons bonded thereto are a fused six-memberaryl ring and n=0 to 4.

Referring to FIGS. 6-8, formulae of substituted or unsubstitutedaromatic 5-member heterocyclic amines or 6-member heterocyclic aminesare shown. Referring to FIG. 6, R3 may be H. R4, R5, R7 and R8 aregenerally independently H, straight chain or branched chain lower alkyl,hydroxyl, amino, or taken together are a fused six-member aryl ring. R6may be H, straight chain or branched chain lower alkyl, hydroxyl, aminoor pyridyl.

Referring to FIG. 7, one of L1, L2 and L3 may be N, while the other L'smay be C. R9 may be H. If L1 is N, R10 may be H.

If L2 is N, R11 may be H. If L3 is N, R12 may be H. If L1, L2 or L3 isC, then R10, R11, R12, R13 and R14 may be independently selected fromstraight chain or branched chain lower alkyl, hydroxyl, amino, orpyridyl.

Referring to FIG. 8, R15 and R16 may be H. R17, R18 and R19 aregenerally independently selected from straight chain or branched chainlower alkyl, hydroxyl, amino, or pyridyl.

Suitably, the concentration of aromatic heterocyclic amine catalysts isabout 10 mM to 1 M. Concentrations of the electrolyte may be about 0.1 Mto 1 M. The electrolyte may be suitably a salt, such as KCl, NaNO₃,Na₂SO₄, NaCl, NaF, NaClO₄, KClO₄, K₂SiO₃, or CaCl₂ at a concentration ofabout 0.5 M. Other electrolytes may include, but are not limited to, allgroup 1 cations (e.g., H, Li, Na, K, Rb and Cs) except Francium (Fr),Ca, ammonium cations, alkylammonium cations and alkyl amines. Additionalelectrolytes may include, but are not limited to, all group 17 anions(e.g., F, Cl, Br, I and At), borates, carbonates, nitrates, nitrites,perchlorates, phosphates, polyphosphates, silicates and sulfates. Nagenerally performs as well as K with regard to best practices, so NaClmay be exchanged with KCl. NaF may perform about as well as NaCl, so NaFmay be exchanged for NaCl or KCl in many cases. Larger anions tend tochange the chemistry and favor different products. For instance, sulfatemay favor polymer or methanol production while Cl may favor productssuch as acetone. The pH of the solution is generally maintained at aboutpH 3 to 8, suitably about 4.7 to 5.6.

Some embodiments of the present invention may be further explained bythe following examples, which should not be construed by way of limitingthe scope of the invention.

Example 1: General Electrochemical Methods

Chemicals and materials. All chemicals used were >98% purity and used asreceived from the vendor (e.g., Aldrich), without further purification.Either deionized or high purity water (Nanopure, Barnstead) was used toprepare the aqueous electrolyte solutions.

Electrochemical system. The electrochemical system was composed of astandard two-compartment electrolysis cell 102 to separate the anode 118and cathode 120 reactions. The compartments were separated by a porousglass frit or other ion conducting bridge 116. A 0.5 M KCl (ElectroMigration Dispersion (END)>99%) was generally used as the supportingelectrolyte 122. A concentration of the desired aromatic heterocyclicamine, such as pyridine, pyridine derivatives, bipyridine, imidazole andimidazole derivatives, of between about 1 mM to 1 M was used.

Referring to FIG. 9, a flow diagram of an example method 140 used in theelectrochemical examples is shown. The method (or process) 140 generallycomprises a step (or block) 142, a step (or block) 144, a step (orblock) 146, a step (or block) 148 and a step (or block) 150. The method140 may be implemented using the system 100.

In the step 142, the electrodes 118 and 120 may be activated whereappropriate. Introduction of the reactants into the cell 102 may beperformed in the step 144. Electrolysis of the reactants into organicproducts may occur during step 146. In the step 148, the organicproducts may be separated from the electrolyte. Analysis of thereduction products may be performed in the step 150.

The working electrode was a steel electrode of a known area. Before andduring all electrolysis, the reactants were continuously introduced intothe electrolyte to saturate the solution. The resulting pH of thesolution was maintained at about pH 3 to pH 8.

Example 2: General Photoelectrochemical Methods

Chemicals and materials. All chemicals used were analytical grade orhigher. Either deionized or high purity water (Nanopure, Barnstead) wasused to prepare the aqueous electrolyte solutions.

Photoelectrochemical system. The photoelectrochemical system wascomposed of a Pyrex three-necked flask containing 0.5 M KCl assupporting electrolyte and a 1 mM to 1M catalyst (e.g., 10 mM pyridineor pyridine derivative). The photocathode was a single crystal p-typesemiconductor etched for approximately 1 to 2 minutes in a bath ofconcentrated HNO₃:HCl, 2:1 v/v prior to use. An ohmic contact was madeto the back of the freshly etched crystal using an indium/zinc (2 wt. %Zn) solder. The contact was connected to an external lead withconducting silver epoxy (Epoxy Technology H31) covered in glass tubingand insulated using an epoxy cement (Loctite 0151 Hysol) to expose onlythe front face of the semiconductor to solution. All potentials werereferenced against a saturated calomel electrode (Accumet). During allelectrolysis, the reactants were continuously introduced to theelectrolyte to saturate the solution. The resulting pH of the solutionwas maintained at about pH 3 to 8 (e.g., pH 5.2).

Referring to FIG. 10, a flow diagram of an example method 160 used inthe photochemical examples is shown. The method (or process) 160generally comprises a step (or block) 162, a step (or block) 164, a step(or block) 166, a step (or block) 168 and a step (or block) 170. Themethod 160 may be implemented using the system 100.

In the step 162, the photoelectrode may be activated. Introduction ofthe reactants into the cell 102 may be performed in the step 164.Electrolysis of the reactants into organic products may occur duringstep 166. In the step 168, the organic products may be separated fromthe electrolyte. Analysis of the reduction products may be performed inthe step 170.

Light sources. Four different light sources were used for theillumination of the p-type semiconductor electrode. For initialelectrolysis experiments, a Hg—Xe arc lamp (USHIO UXM 200H) was used ina lamp housing (PTI Model A-1010) and powered by a PTI LTS-200 powersupply. Similarly, a Xe arc lamp (USHIO UXL 151H) was used in the samehousing in conjunction with a PTI monochromator to illuminate theelectrode at various specific wavelengths.

A fiber optic spectrometer (Ocean Optics S2000) or a siliconphotodetector (Newport 818-SL silicon detector) was used to measure therelative resulting power emitted through the monochromator. The flatbandpotential was obtained by measurements of the open circuit photovoltageduring various irradiation intensities using the 200 watt (N) Hg—Xe lamp(3 W/cm²-23 W/cm²). The photovoltage was observed to saturate atintensities above approximately 6 W/cm².

For quantum yield determinations, electrolysis was performed underillumination by two different light-emitting diodes (LEDs). A blue LED(Luxeon V Dental Blue, Future Electronics) with a luminous output of 500milliwatt (mW)+/−50 mW at 465 nanometers (nm) and a 20 run full width athalf maximum (FWHM) was driven at to a maximum rated current of 700 mAusing a Xitanium Driver (Advance Transformer Company). A Fraencollimating lens (Future Electronics) was used to direct the outputlight. The resultant power density that reached the window of thephotoelectrochemical cell was determined to be 42 mW/cm², measured usinga Scientech 364 thermopile power meter and silicon photodetector. Themeasured power density was assumed to be greater than the actual powerdensity observed at the semiconductor face due to luminous intensityloss through the solution layer between the wall of thephotoelectrochemical cell and the electrode.

Example 3: Analysis of Products of Electrolysis

Electrochemical experiments were generally performed using a CHInstruments potentiostat or a DC power supply with current logger to runbulk electrolysis experiments. The CH Instruments potentiostat wasgenerally used for cyclic voltammetry. Electrolysis was run underpotentiostatic conditions from approximately 6 hours to 30 hours until arelatively similar amount of charge was passed for each run.

Gas Chromatography. The electrolysis samples were analyzed using a gaschromatograph (HP 5890 GC) equipped with a FID detector. Removal of thesupporting electrolyte salt was first achieved with an AroberliteIRN-150 ion exchange resin (cleaned prior to use to ensure no organicartifacts by stirring in a 0.1% v/v aqueous solution of Triton X-100,reduced (Aldrich), filtered and rinsed with a copious amount of water,and vacuum dried below the maximum temperature of the resin(approximately 60° C.) before the sample was directly injected into theGC which housed a DB-Wax column (Agilent Technologies, 60 m, 1micrometer (μm) film thickness). Approximately 1 gram of resin was usedto remove the salt from 1 milliliter (mL) of the sample. The injectortemperature was held at 200° C., the oven temperature maintained at 120°C., and the detector temperature at 200° C.

Spectrophotometry. The presence of formaldehyde was also determined bythe chromotropic acid assay. Briefly, a solution of 0.3 g of4,5-dihydroxynaphthalene-2,7-disulfonic acid, disodium salt dihydrate(Aldrich) was dissolved in 10 mL deionized water before diluting to 100mL with concentrated sulfuric acid. For formaldehyde, an aliquot of 1.5mL was then added to 0.5 mL of the sample. The presence of formaldehyde(absorbency at 577 nm) was detected against a standard curve using an HP8453 UV-Vis spectrometer. For formic acid, a 0.5 mL aliquot of samplewas first reduced with an approximately 100 mg piece of Mg wire and 0.5mL concentrated hydrochloric acid (added slowly in aliquots over a 10minute period) to convert to formaldehyde before following thechromotropic acid assay as described above.

Nuclear Magnetic Resonance. NMR spectra of electrolyte Volumes afterbulk electrolysis were also obtained using an automated BrukerUltrashield™ 500 Plus spectrometer with an excitation sculpting pulsetechnique for water suppression. Data processing was achieved usingMestReNova software.

Selective hydrodimerization carbonyl-containing organic molecules, suchas aldehydes and carboxylic acids, may be performed in the cell 102. Forinstance, some two-carbon molecules such as an acetaldehyde may behydrodimerized into butanone (methyl ethyl ketone) or butanol.Similarly, a carboxylic acid such as butyric acid may be hydrodimerizedto octanone or octanol.

Selective reduction of carboxylic acids to aldehydes and/or alcohols andthe reduction of aldehydes to alcohols may also be performed in the cell102. Other carbonyl groups, such as ketones, may also be reduced tohydroxyl groups. The selectivity of the process generally maximizesefficiency and ease of product extraction relative to existing processesused for organic chemical production. Some embodiments do not operate athigh temperatures, high pressures or high acidity. Biologically-producedchemicals with carbonyl groups may be converted toenvironmentally-friendly alcohol fuels, thereby reducing greenhouse gasemissions. Conversion of small molecules to longer-chain molecules,generally reduces the costs of upgrading small molecules into high valueproducts. A variety of C2, C4, C6, C8 organic molecules may be produced.

Some embodiments of the present invention generally provide for newcathode materials and new electrolyte materials. Specific combinationsof the cathode materials, the electrolytes and the catalysts may be usedto get a desired organic product. Process conditions may be controlledto maximize conversion efficiency and selectivity. Cell parameters maybe selected to minimize unproductive side reactions like H₂ evolutionfrom water electrolysis. Choice of specific configurations ofheterocyclic amine catalysts with engineered functional groups may beutilized in the system 100 to achieve high faradaic rates. Processconditions described above may facilitate long life (e.g., improvedstability), electrode and cell cycling and product recovery.

Cathode, catalyst and electrolyte combinations may be used toselectively electrohydrodimerize carbonyl-containing compounds to avariety of valuable organic chemicals. The cathode, catalyst andelectrolyte combinations may also be used to selectively reduce carbonylgroups, including aldehydes, to alcohols and carboxylic acids toaldehydes and/or alcohols. The relative low cost and abundance of thecombinations disclosed above generally opens the possibility ofcommercialization. The processes described may operate at atmosphericpressure, ambient temperature, uses water as a solvent and features mildpH (e.g., generally greater than pH 4). The features generally mean thatabundant, low-cost materials may be used to build plants incorporatingsome embodiments of the present invention. Furthermore, the process maybe stable over time.

In an electrochemical system with fixed cathodes, the electrolyte and/orcatalyst may be altered to change the organic product mix. The cathodesmay be swapped out in a modular electrochemical system to change theorganic product mix. In a hybrid photoelectrochernical system, thecathode or anode may be a photovoltaic material. Plant operating inconjunction with biological production of simple carbonyl-containingchemicals such as acetaldehyde, lactic acid, citric acid, etc. mayinclude the system 100 to covert the chemicals into other useful organiccompounds. Biologically produced chemicals may be converted into longerchain chemicals and products such fuels, solvents and the like.

While the invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the scope of the invention.

The invention claimed is:
 1. A method for heterocycle catalyzedhydrodimerization of carbonyl-containing molecules, comprising the stepsof: (A) introducing said carbonyl-containing molecules into a solutionof an electrolyte and a heterocycle catalyst in a dividedelectrochemical cell, wherein (i) said divided electrochemical cellcomprises an anode in a first cell compartment and a cathode in a secondcell compartment, (ii) said cathode hydrodimerizing saidcarbonyl-containing molecules into at least one organic product; (B)varying which of said organic products is produced by adjusting one ormore of (i) a cathode material, (ii) said electrolyte, (iii) saidheterocycle catalyst, (iv) a pH level and (v) an electrical potential;and (C) separating said organic products from said solution, whereinsaid heterocycle catalyst is one or more of amino-thiazole, aromaticheterocyclic amines with an aromatic 5-member heterocyclic ring,aromatic heterocyclic amines with 6-member heterocyclic ring, azoles,benzimidazole, bipyridines, furan, imidazoles, imidazole related specieswith at least one five-member ring, indoles, pyridines, pyridine relatedspecies with at least one six-member ring, pyrrole, thiophene andthiazoles.
 2. The method according to claim 1, wherein said electrolyteis at least one of Na₂ SO₄, KCl, NaNO₃, NaCl, NaF, NaClO₄, KClO₄,K₂SiO₃, CaCl₂, a H cation, a Li cation, a Na cation, a K cation, a Rbcation, a Cs cation, a Ca cation, an ammonium cation, an alkylammoniumcation, a F anion, a Cl anion, a Br anion, an I anion, an At anion, analkyl amine, berates, carbonates, nitrites, nitrates, phosphates,polyphosphates, perchlorates, silicates, sulfates, and a tetraalkylammonium salt.
 3. The method according to claim 1, wherein said organicproducts comprise one or more of butanone, butanol, octanone andoctanol.
 4. The method according to claim 1, wherein saidcarbonyl-containing molecules comprise one or more of acetaldehyde,butyric acid and lactic acid.